Glyphosate is well known in the art as an effective post-emergent foliar-applied herbicide. In its acid form (N-(phosphonomethyl)glycine), glyphosate has the following structure:
Glyphosate acid is relatively insoluble in water (about 1.16 wt. % at 25° C.). For this reason it is typically formulated as a water-soluble salt. For example, herbicidal concentrate compositions and application formulations containing, for example, the sodium, potassium, ammonium, isopropylamine, or monoethanolamine salts of glyphosate are well known in the art.
Herbicidal compositions and formulations comprising glyphosate or glyphosate salt are useful for suppressing the growth of, or killing, unwanted plants such as grasses, weeds and the like. Glyphosate is typically applied to the foliage of the target plant. After application, glyphosate is absorbed by the foliar tissue of the plant and translocated throughout the plant. Glyphosate noncompetitively blocks an important biochemical pathway which is common to virtually all plants, but which is absent in animals. Although glyphosate is very effective in killing or controlling the growth of unwanted plants, the uptake (i.e., absorption) of glyphosate by plant foliar tissue and translocation of glyphosate throughout the plant is relatively slow. Visual symptoms that a plant has been treated with glyphosate may not appear until one week or more after treatment.
Dicamba has proven to be a particularly effective auxin herbicide. In its acid form, dicamba has the following structure:
Like glyphosate, dicamba is typically formulated as a salt, such as the sodium, potassium, diethanolamine, isopropylamine, diglycolamine, or dimethylamine salt.
Generally, auxin herbicides such as dicamba mimic or act like natural auxin plant growth regulators. Auxin herbicides appear to affect cell wall plasticity and nucleic acid metabolism, which can lead to uncontrolled cell division and growth. The injury symptoms caused by auxin herbicides include epinastic bending and twisting of stems and petioles, leaf cupping and curling, and abnormal leaf shape and venation.
Off-site movement is sometimes associated with dicamba and other auxin herbicides. Under certain conditions of application, dicamba can migrate from the application site to adjacent crop plants, such as soybeans and cotton, where contact damage to sensitive plants can occur. Various strategies have been suggested to reduce off-site movement of dicamba including formulating dicamba in the form of certain mineral or amine salts, encapsulating dicamba with a polymeric coating, and complexing with a polybasic polymer.
Tank mixes of dicamba and glyphosate are known in the art. For example, an herbicidal concentrate containing 480 grams acid equivalent per liter (g a.e./l) of the dimethylamine salt of dicamba, sold under the trade name BANVEL, is available from BASF. As used herein, the term “acid equivalent” or “a.e.” refers to the amount of herbicide present without taking into account the weight of the counter-ion of the salt species present. The package instructions for use of this concentrate of dicamba indicate that dicamba can be tank mixed with other diluted herbicides including glyphosate. Tank mixing of dicamba and glyphosate according to these instructions provides a spray solution having a total herbicide concentration up to about 100 g a.e./l. Patent literature also mentions herbicidal compositions containing glyphosate and dicamba. For example, see U.S. Patent Application Publication No. US 2006/0019828 A1 and U.S. Pat. Nos. 6,277,788 and 6,455,473.
Addition of glyphosate to some tank mixes of dicamba has been known to negatively affect dicamba volatility and increase off-site movement of dicamba. Accordingly, there remains a need for glyphosate compositions that can be tank mixed with dicamba that will reduce the effects on dicamba volatility resulting from the incorporation of glyphosate. Similarly, there remains a need for a tank mix and method of preparing the tank mix, which has an acceptable dicamba volatility profile.
Further, with the development of transgenic plants including stacked glyphosate-tolerant and dicamba-tolerant traits, tank mix compositions containing a combination of glyphosate and dicamba are particularly beneficial and convenient for control of unwanted plants. Thus, there is a need for concentrate compositions containing glyphosate that can be economically produced while having sufficient stability and that are formulated to provide effective spray formulation solutions for application to unwanted plants. There also remains a need for methods of preparing glyphosate/dicamba tank mixes that reduce or eliminate the increase in dicamba volatility as a result of adding glyphosate.
As will be clear from the disclosure that follows, these and other benefits are provided by the present invention.